This invention provides a method and apparatus for magnetically braking a flow of molten metal to a metal caster. The invention has particular but not exclusive application to braking or retarding a falling flow of molten metal of a twin roll metal strip caster.
In a twin roll caster molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term "nip" is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electro-magnetic barriers have also been proposed.
Although twin roll casting has been applied with some success to non-ferrous metals which solidify rapidly on cooling, there have been problems in applying the technique to the casting of ferrous metals. One particular problem has been the need to ensure a very even metal flow distribution across the width of the nip since even minor flow fluctuations can cause defects when casting ferrous metals. Previous proposals to achieve the necessary even flow have involved the provision of baffles and filters or inclined impingement surfaces in the delivery nozzle to reduce the kinetic energy of the falling molten metal in such a way as to produce a smooth even flow at the nozzle outlet. However these proposals have all involved impingement of a free falling stream of metal with stationary surfaces in the nozzle and it has proved difficult to achieve a controlled retardation of the molten metal while maintaining a smooth, even flow. The present invention can be applied to this problem to achieve magnetic braking of a falling stream of molten metal in the metal delivery system. It will be appreciated from the ensuing description however that the invention is not limited to this application and it may be applied to the braking of falling metal streams in other kinds of casters such as single roll drag casters, belt casters and thin slab casters.